Unlike its predecessor and unfriendlier Wikipedia, it's the WORLDS LARGEST COLLABORATIVE HOW-TO MANUAL that anyone can edit. Many people come together as a global community of volunteers to help contribute daily. Any patrolling/editing/new article boosting you do speaks volumes to the community.

Example 1: "Oh dude, some nasty language in that edit, I'm gonna roll back changes to the last good edit."

Example 2: "I see a ton of spelling/grammar/punctuation/sentence structure mistakes in this article, im going to go ahead and press the edit button on this article now to enlighten them, then perhaps it will even have the chance at becoming a featured article! Horray!"

Example 3: "Did you see my wikiHow about How to be a Goth?" "No, but you should read my article on How to be Preppy instead."

wikiHow is an online manual on how to do anything. When not referencing the site directly, you will often hear the term used to mean "figure it out yourself" or as a passive aggressive way to make a comment.

Referencing the site directly
Person 1: Does anyone know how to get a wine stain out of carpet?
Person 2: Look it up on wikiHow!

A collaborative how-to website which is written by completely random people. You can write and edit articles, even without logging in. The majority of its population are obviously 10 year olds who have no idea how to write. The owners of the website actually profit off of the volunteer work by WikiHow's users which is pretty messed up. The authors at WikiHow must think that everyone is a total idiot because the articles they write are designed retards that have no idea what they're doing. Vandals and trolls are common and will probably delete your article or replace its contents with something inappropriate if they come across it.

A website that has a lot of how-to articles written and edited by HTML noobs. Whenever you make a how-to article somebody will edit it and make your article you took a lot of time to write dumb so you edit it back to what you wrote but then they edit it again. A lot of times they have bad grammer and write stupid stuff in your article so all you want to do is grab them by the neck and bash their head into every object in the room you're in and kill them.

Bob wrote a new wikiHow article but some dude called Jim that has a user page that is all screwy looking that practically screams he's an HTML noob took off everything Bob took the time to write and added retarded stuff so Bob edited it back to what he wrote but then Jim the noob did the same thing again.
Bob: WTF?
Jim: Haha n00b i pwnz yoo!!!!111!!!!!!!! i mak yoor artikle all messed up!!111!!!! hahaha roflcopter lulz!!11!!!!!11one!!!!!11oneone!